Is it only moving in terrain which disorders a unit or merely being in the terrain?

Last night I deployed some FP in difficult going(not saying it was a great decision) and my reading of the rules was that it was only moving which would cause disorder, but my opponent last night was sure that they were disordered from the start.

And if I move to leave the difficult going I am also not disordered I think. (3.1.1 p3) But what qualifies as "leaving"? Does that mean I must finish partially outside the terrain with my initial half speed move? Or must I finish more than half outside the terrain?

One thing Cardy forgot to mention was the supporting archers (T) in the large group. I believe archers are disordered in difficult going for shooting as well as movement. Does this also apply to large groups. In the Chinese lists large groups of FL/T move and fight as T in difficult going therefor I assume they are disordered for shooting as well. Also although I agree the FP are not disordered if stationary I do think that they are disordered for fighting while in difficult going.

The unit must fully exit the disordering terrain to escape the effect.

I don't believe that FP are disordered for fighting in difficult terrain. Again it is moving that disorders units in disordering terrain. It does mean that anytime FP attacks in broken or difficult terrain they do so disordered because attacking requires moving. The notes in the Chinese lists for large FL/T units makes the units T for moving/disordering to my reading.

The QRS states 'Disordered, Half speed' which would indicate that you are disordered even if stationary. That is just my interpretation. T look to be disordered for moving and shoot disordered, which is a stationary action. Also I cannot see FP forming a nice straight line and locking shields when the guy to your left is a ten foor wide bush, (with slightly more intelligence than the guy to it's right).

As Accard noted, leaving disordering terrain doesn't cause disorder, This rule would make no sense if standing in the terrain caused automatic disorder, as the unit could never get in good order before leaving the terrain. The act of shooting can never cause disorder.

If you have 2 units of FP (A & B) approaching each other in a wood A moves then B approaches within 2.5 cm. If in the next move A charges B then B in considered to be stationary and therefor not disordered. It does not make sense.

No, B is disordered as it moved in difficult terrain - unless it passed a subsequent discipline test to reorder. You don't automatically re-order by standing still. Nor do you get disordered by standing still.